Mobile devices such as, but not limited to, mobile phones, smart phones, personal digital assistants (PDAs), tablets, laptops or other electronic devices, etc., increasingly include voice recognition systems to provide hands free voice control of the devices. Although voice recognition technologies have been improving, accurate voice recognition remains a technical challenge.
A particular challenge when implementing voice recognition systems on mobile devices is that, as the mobile device moves or is positioned in certain ways, the acoustic environment of the mobile device changes accordingly thereby changing the sound perceived by the mobile device's voice recognition system. Voice sound that may be recognized by the voice recognition system under one acoustic environment may be unrecognizable under certain changed conditions due to mobile device motion or positioning.
More specifically, the mobile device acoustic environment impacts the operation of signal processing components such as microphone arrays, noise suppressors, echo cancellation systems and signal conditioning that is used to improve voice recognition performance. When a mobile device is placed on or near a table or other surface, the result is a change of the transfer function between the mobile device microphones, the relative signal strength and phase of the microphone signals, and creation of additional reflections, all of which negatively impact the operation of the signal processing components, rendering them sub-optimal. For example, where a microphone array is used, changes in the acoustic environment results in undesirable changes in the array directivity, and increases pick-up of undesired sound sources. These considerations impact voice recognition systems and also other mobile device operations such as speaker phone operation since changes in the acoustic environment will impact the echo canceller among other things.